This paper proposes a novel communication protocol, called Many-to-One Sensors-to-Sink (MOSS), tailored to wireless sensor networks (WSNs). It exploits the unique sensors-to-sink traffic pattern to realize low-overhead medium access and low- latency sensors-to-sink routing paths. In conventional schedule-based MAC protocols such as S-MAC, sensor nodes in the proximity of the event generate reports simultaneously, causing unreliable and unpredictable performance during a brief but critical period of time when an event of interest occurs. MOSS is based on time division multiple access (TDMA) that avoids energy waste due to collisions, idle listening and overhearing and avoids unreliable behavior mentioned above. A small test-bed consisting of 12 TelosB motes as well as extensive simulation study based on ns-2 have shown that MOSS reduces the sensor-to-sink latency by as much as 50.5% while consuming only 12.8 ∼ 19.2% of energy compared to conventional TDMA algorithm.